Why does the gas motor come on so soon?

<div class='quotetop'>QUOTE(Katz @ Nov 15 2006, 10:01 PM) [snapback]349872[/snapback]</div>

My assumption has always been that it does that to make sure it can start the engine. It would rather suck to get a mile or two away, have the battery run out, and then find out the engine won't start.

 

<div class='quotetop'>QUOTE(Katz @ Nov 15 2006, 10:01 PM) [snapback]349872[/snapback]</div>

Hi Katz,

The engine comes on fast, because all the electricity in the battery is generated by the engine, and the electric acceleration is about 66 percent efficient. So, the total efficiency from fuel to accelleration is worse by electric means, than by engine. The efficiency tank to wheel for engine is Engine Efficiency * Transmission Eficiency * Final Drive Efficiency. The electric efficiency tank to wheel is Engine Efficiency * Transmission Efficiency * Generator Efficiency * Electric Drive Efficiency * Motor Efficiency * Final Drive Efficiency. Or Electric Efficiency = Tank-to-Wheel Efficiency * Generator Efficiency * Electric Drive Efficiency * Motor Efficiency . Since the Generator to Motor loop is about 54 percent efficient, its best to put the engine output directly through the transmission to the final drive whenever the requirement puts the engine into an efficient level. Accellerating takes allot of power, and the engine will be in efficient output level during that requirement.


The Hybrid advantage comes along at cruise when the power required is way to low for the engine to run efficiently. This is typically 25 to 40 mph in the Prius, but more like 25 to 60 mph in an Otto engine car, because of the lower part throttle efficiency. In this speed range its easy to drop into glide (no arrows) , or use the electric drive.

The electricity comes from regeneration, and the output requirement is low but too much for the battery alone - then the system runs the engine power to both the battery and the wheels. This increases the engine power output into a more efficient level.

This is the kinda the 2-bit technology basis for the Hybrid car. Hope it was a good answer to your question.

For good mileage it best to avoid electric acceleration unless, its very low accelleration, or the battery is up in the green-bars level. If the battery is up in the green level, the car is going use the battery anyway to get the level down. Preserving battery charge for cruise is best, because the current levels are lower in the interconnects, motor and motor drive, which disipates less heat, and gets better distance per KWH.

 

I thought the ICE started for the first few minutes, only to preheat the Catalytic Converter.

 

<div class='quotetop'>QUOTE(mojo @ Nov 15 2006, 06:08 PM) [snapback]349898[/snapback]</div>

I agree with mojo, that the computer 'decides' to turn the engine on soon aftwer power-up mostly to warm itself and the especially to warm up the catalytic converter so that the emmissions are as low as possible.

Also, even if the ICE and catalytic converter are warmed up nicely, the engine might decide to come on when you are stationary if you have the heater or A/C on and/or if the 200 Volt battery is low.

Cheers

 

<div class='quotetop'>QUOTE(Fibb222 @ Nov 15 2006, 11:15 PM) [snapback]349899[/snapback]</div>

Except that if you just sit there in the parking space, the engine starts 7 seconds after you turn the car on and runs for about 30 seconds and then shuts off again. I doubt it did much warming up of anything in 30 seconds, at least not to anything resembling normal operating temperatures.

So why not wait until power from the engine is actually needed before starting the engine. That was in essense the question of the original poster.

 

<div class='quotetop'>QUOTE(Marlin @ Nov 16 2006, 07:59 AM) [snapback]350063[/snapback]</div>

You're right about normal operating temperature of the engine which is reflected in the temperature of the engine coolant. However, the cat converter is heated by the exhaust gas which is much hotter than the coolant and can raise the temperature of the cat converter in a matter of seconds and not minutes.

 

<div class='quotetop'>QUOTE(Marlin @ Nov 16 2006, 08:59 AM) [snapback]350063[/snapback]</div>

It's warming up the catalytic converter. The first priority for the Prius is low emissions. Fuel economy comes second.

Tom

 

<div class='quotetop'>QUOTE(donee @ Nov 15 2006, 08:00 PM) [snapback]349894[/snapback]</div>

First, all the electricity in the batteries is not generated by the engine. Some of it is, but some of it also comes from the regenerative braking. How much of each is highly dependent on the individual driving style.

As for the hybrid advantage, it once again is much more complex than that. First advantage: the ICE stops running when it doesn't need to. Second advantage: Electric power for acceleration assistance. Third advantage: recapturing of lost kinetic energy through regenerative braking. It's a combination of these and many, many more factors that make the car run so well.

As far as preserving battery charge for cruise... using it for gliding is much better. The most efficient way to drive the car is to "Pulse" up to speed (using the ICE, with a little regen to the batteries) then "Glide" down a bit (ie with no arrows on the energy display). Unfortunately the glide portion does use a little electricity, thus you need a little bit of regen when pulsing.

As far as cruising (I assume you're referring to highway speeds) - the battery SOC doesn't change much when you're at speed. in fact, if you find a perfectly flat section of road and are cruising along at 65, you probably won't see much, if any, action going on with the batteries. When i'm at 6 bars and on the highway, generally it'll either just be all ICE (at very low RPM's giving good mileage) or the battery will be constantly flip flopping between providing and storing power.

As for the OP:
The ICE does start up 7-8 seconds after you start the car, every time. this is in order to heat up the catalytic converter and the coolant. You should also find the guide on here for the 5 stages of Prius operation - it discusses the details behind warming up and progressing through the stages to the point where the ICE can turn on and off at any time. (as opposed to just turning off after you've come to a complete stop, like it does in earlier stages)

 

<div class='quotetop'>QUOTE(eagle33199 @ Nov 16 2006, 10:38 AM) [snapback]350096[/snapback]</div>

Unless you push your Prius up a hill before you start, all of the electricity in the battery comes from the ICE. The electricity generated by regen braking is converted from kinetic energy that was imparted by the ICE; all of the energy comes from the ICE. It takes many paths getting to the road, buy it all comes from the ICE. It can go directly to the road through the PSD; through MG1 to MG2; stored in the battery and later through MG2; or stored as kinetic energy in the Prius, then to the battery through regen, then back through MG2. Regardless, it all starts as gasoline burned in the ICE.

Tom

 

<div class='quotetop'>QUOTE(qbee42 @ Nov 16 2006, 08:52 AM) [snapback]350101[/snapback]</div>

Yes, in the grand scheme of things, however the implication in the post i was referring to didn't include the recaptured energy from regenerative braking. In fact, the entire paragraph was geared towards the efficiencies encountered when charging the batteries directly from the ICE, and never mentioned regenerative braking. While i definitely do realize, and agree with you, that ultimately all of the energy in the batteries started out as gas, i guess i was looking at it from a different point of view. From the point of view of locomotive energy, the ICE can provide energy directly to the road, moving the car. it can also provide energy to the batteries, which is then later used to move the car, or energy to the motor which is used to move the car. All of these are "primary" ways to cause the car to move - direct, unavoidable costs of movement. regenerative braking, on the other hand, captures some of the energy that was already spent. So if the energy was already used for locomotive force, recapturing it and using it again essentially makes it "free energy", which leads to the view point that recaptured energy from regenerative braking doesn't really count.

I'm sure i didn't explain that as well as i wanted to... but the short is that I agree that it all does come from the ICE, but when you start double counting it through regenerative braking it gets obfuscated. I guess it's like getting cash back on a credit card - The cash all comes from you, but you view it as being free money for buying something you were going to buy anyways.

 

<div class='quotetop'>QUOTE(eagle33199 @ Nov 16 2006, 11:38 AM) [snapback]350096[/snapback]</div>

Hi Eagle,

You assume wrong.

I was talking about cruising along at 30 to 45 mph city streets. Sorry I did not make that clear.

 

<div class='quotetop'>QUOTE(eagle33199 @ Nov 16 2006, 11:55 AM) [snapback]350139[/snapback]</div>

I was pretty sure that's what you meant. I just wanted to clarify that the ICE is the only source of energy.

In keeping with what you said above, with our cold weather this time of the year, I see the SOC in the green much more often than during the summer. The ICE has to run to make heat, so the Prius might as well do something useful with the energy and charge the battery.

Tom

 

<div class='quotetop'>QUOTE(qbee42 @ Nov 16 2006, 06:52 AM) [snapback]350101[/snapback]</div>

I'm with qbee42 on this and his previous post to this one. All power comes from the ICE and the emissions is a priority.

 

<div class='quotetop'>QUOTE(qbee42 @ Nov 16 2006, 11:18 AM) [snapback]350084[/snapback]</div>

However, if catalytic converter heats up in seconds, then why bother to do it while the car is just sitting there in park? Why not wait until power is required from the engine.

What benefit is there in producing emissions while performing no work just to heat up the catalytic converter when you could delay that activity until there is work to be performed.

That's the question to be answered. Warming up the engine or the catalytic converter is not a reasonable excuse to start the engine while the car is just sitting there in Park. Why not at least wait until the car is placed in Drive? Why not wait until the engine is actually needed to move the car?

And, most people are already in motion 7 seconds after the car is turned on, so it can't be too important to start the engine before the engine comes under significant load, because 90+% of the time it's already under load when the engine does come on the first time.

So, given that, the question still stands, why does it bother to start the engine 7 seconds after you turn on the car, even if the car is still sitting in Park? Why not just wait until the engine needs to be started?

 

<div class='quotetop'>QUOTE(Marlin @ Nov 16 2006, 11:02 AM) [snapback]350265[/snapback]</div>

It might be more than a few seconds to heat up the catalytic converter - perhaps closer to a minute or two. And yes, I'd also like to know the exact technical reasons behind the programming but I don't really doubt that Toyota's design was deliberate and for a good reason.

 

<div class='quotetop'>QUOTE(Fibb222 @ Nov 16 2006, 04:53 PM) [snapback]350314[/snapback]</div>

In most cases I think it is a fair assumption that the engine will be needed very soon after "Ready" lights up. During the 8 or so seconds delay, the thermos is dumping its hot water into the engine circuit. With out starting the engine, that begins to cool off very quickly, especially in cold weather.

If the car held off the thermos dump, it would be losing some of that preheat benefit if it had to light up the engine on a power demand with no time for the thermos dump.

Since I added a Scan Guage and have been watching the coolant temperature, I see that a side effect of using EV mode for the last few hundred yards into the parking lot at work gives a temperature drop of 20 degress F or more in the coolant pumped back into the thermos. That means less of a boost to engine temperature when I leave for home in the evening and a longer inefficent warm-up time. In the summer it is minor, in the winter it seems like quite a hit. TANSTAAFL.

- Tom

 

<div class='quotetop'>QUOTE(Katz @ Nov 15 2006, 10:01 PM) [snapback]349872[/snapback]</div>

Hi All,

Some of you read the words above differently. He is asking why the Prius would not let him ACCELLERATE more briskly in electric drive. This is the question I endevoured to answer.

 

<div class='quotetop'>QUOTE(donee @ Nov 16 2006, 08:50 PM) [snapback]350517[/snapback]</div>

The battery doesn't last very long, nor is it efficient to draw power from the battery just to turn around and put it back in. The battery is there mostly to store power from regen braking and to provide a short burst of power for hill climbing, passing, and the like. When you stomp on the gas, the Prius assumes you are going to need some serious power, so the ICE kicks on. It has no way of guessing whether you intend to stomp on the gas for two seconds or two minutes. In most cases, it's more efficient to turn on the ICE, so that's what it does.

Tom

 

Why start the ICE 7 seconds after power up? Besides preparing for a drive by preheating things, I belive the other reason is a systems check.

Why use ICE during acceleration? To get the power you demand. Sure, MG2 is pretty powerful, but remember what powers MG2: battery and MG1. MG1 only provides power when ICE is running. The battery can only provide so much power and for only so long. So with gentle acceleration, MG2 and battery is quite efficient. Any more than that, and ICE is needed to provide more power.
Now ICEs are never really efficient at lower RPMs, and at lower ground speeds, a direct connected ICE will probably run at a low RPM. So the synergy drive instead runs ICE at a higher RPM, sends some of that power directly to the wheels, the remaining goes to MG1 to send to MG2.